Referring to FIG. 12, a conventional cage 100 for a roller bearing will be described. FIG. 12 shows the cross-sectional shape of one of both pillar portions which face each other in a circumferential direction in a pocket 101. The shape of the other pillar portion is also the same. Each pillar portion has a plurality of bent portions 102, 103 and 104 which are alternately bent in the width direction of the cage to hold the diameter (the diameter of a pitch circle of the roller, hereinafter referred to as “roller PCD”) of a circle line connecting centers of the roller in the thickness direction of the cage. The bent portions 102 to 104 are respectively provided with roller stopping portions 105 to 107 protruding in the shape of a claw or a tongue piece into the pocket hole 101. A roller 108 is retained within the pocket 101 by the roller stopping portions 105 to 107 (refer to Patent Literatures 1 and 2).
According to the configuration of the conventional cage 100 as described above, in the manufacturing processes of the cage, there is a pocket forming process of punching an annular blank made of a steel plate which is alternately bent in the shape of “W” in cross section in the width direction, thereby forming pockets 101. In this process, the roller stopping portions 105 to 107 are simultaneously formed such that portions of the bent portions 102 to 104 protrude toward the pocket 101. Thus, flat regions which are relatively long in the width direction of the cage are required in the bent portions 102 to 104 for formation of the roller stopping portions 105 to 107. For this reason, the interval of the bent portions 102 to 104 in the width direction of the cage becomes long. As a result, there is a limit to shortening the interval of the roller stopping portions 105 to 107 in the width direction of the cage. It is thus difficult to shorten the width of the pocket in the width direction of the cage beyond the limit and to manufacture a cage capable of retaining a roller (short roller) whose length is short. Further, assuming that the interval of the roller stopping portions 105 to 107 and the plate thickness thereof are represented by “D” and “T”, respectively, in the configuration of the conventional cage, the cage thickness (height) of 2T+D is necessary. As a result, even if the interval D can be shortened in response to the diameter of a roller, the thickness of the cage cannot be reduced to less than 2T. Thus, this 2T becomes a limit to miniaturization of the cage in the thickness direction. Consequently, it is difficult to miniaturize the cage beyond the above limit.
Patent Document 1: JP-UM-A-64-55322
Patent Document 2: JP-UM-A-03-51225